Two-dimensional single-phase and two-phase models were used to investigate the behavior of a PEM fuel cell under different steady-state conditions. It was observed that,a high value of the in-plane thermal conductivity for the GDLs is essential for achieving smaller temperature gradients. This was determined to be even more important for thin GDLs. At a given fixed voltage and high humidity inlet conditions, the fuel cell generates maximum current density for bipolar plates with narrow ribs and for GDLs with low
through-plane and high in-plane thermal conductivities. It is also predicted that for low
humidity operating conditions, the fuel cell generates maximum current density if the GDL is tailored to have high through-plane thermal conductivity and wider ribs near the inlet and progressively decreasing through-plane thermal conductivity and narrower ribs at distances away from the inlet. Additionally, analysis of the effects of anisotropic electrical resistivity shows that, in case of GDLs with high anisotropic thermal conductivity, the maximum and minimum temperatures in a cathode catalyst layer correlate with the average current density and not the local current density.
A three-dimensional model was also developed to analyze external heating techniques used for PEMFC startup. The analysis shows that the thermal mass of the bipolar plates is an important factor affecting the startup time. Therefore, thin, flexible,planer electric heaters are better suited for PEMFC heating applications than the cartridge heaters. Also, GDLs with low through-plane thermal conductivities and high in-plane thermal conductivities are able to reduce the startup time when used in conjunction with a heating element embedded within the GDL.